The present invention relates to stainless spheroidal carbide cast iron and its object is to provide stainless spheroidal carbide cast iron which has special characteristics such as corrosion-resistance, heat-resistance, abrasion-resistance, thoughness and processing ability. Such stainless spheroidal carbide cast iron improving its characteristics such as heat-resistance and corrosion-resistance can be applied within a wide areas of industries such as chemical industry, machinery, shipping and petrochemical industry which efficiency and functions are getting high in accordance with the development of the industries.
Up to the present, pieces of apparatus such as boiler equipments and chemical plant instruments used in high temperature environment require materials with heat-resistance and corrosion-resistance. However in these days, more resistance under more severe conditions is required as the advancement of high temperature equipments, better functioning and becoming highly efficient in each area of the industries including chemical industry are remarkable. For example, in an area of injection molding of engineering plastic, ceramic, reinforcements like FPR and all kinds of additives are added into the resin in order to raise strength, fire-resistance and abrasion-resistance of resin moldings. As a result, with the ceramic being fragile, the resin molding system is easy to be abraded because of the reinforcement within the cylindrical resin, and it further becomes easy to corrode with a corrosive gas generated from the additives. Also, since shapes of parts manufactured in all kinds of industries such as car industry are getting complex, abrasion of manufacturing apparatuses has become more severe than ever.
With the industries developing dramatically, strength, heat-resistance, abrasion-resistance, corrosion-resistance, and processing ability of materials are required to be higher than prior ones in surroundings where the apparatuses are used severely.
Firstly, a usage of white cast iron which is strong cast iron can be considered in order to obtain outstanding abrasion-resistance. Said white cast iron consisting no graphite within its organization has a defect that it is very fragile, being formed with pearlite and cementite. Therefore, it is not easy to obtain outstanding abrasion-resistance in the usage of the white cast iron. That""s why a usage of spheroidal graphite cast iron with toughness, conquering the defect of white cast iron, is on trial.
Said spheroidal graphite cast iron wherein a configuration of flake graphite crystallized in its organization is spheroidal in shape has outstanding toughness because the configuration of crystallized substance in the organizations of metallic materials gives a great influence on toughness. That is to say that generally, the configuration of a crystallized substance bonds covalently or couples electro statically, becoming a facet and platen in shape always when it has a strong anti-metal characteristic. In this circumstance, thoughness is weak. Contrarily, when a characteristic of metal is strong, the configuration of a crystallized substance bonds metallically, becoming a nonfacet granular or spheroidal dendrite. In these circumstances, toughness is strong due to a dispersion of force even when being given an impact from an outside. In a case of the spheroidal graphite cast iron, it has outstanding toughness because the configuration of the flake graphite crystallized within the organization of cast iron is made to be spheroidal in shape with more than 0.04% of magnesium (Mg) being composed. However, it is difficult to hold both strong toughness and abrasion-resistance.
On the other hand, the present inventors have already disclosed that alloy cast iron with outstanding abrasion-resistance and impact-resistance can be obtained by crystallized spheroidal or granular V-C system carbide and Fe-Cr system carbide within the organization of cast iron in Japanese patent application No.9-307951.
Said spheroidal graphite cast iron has outstanding abrasion-resistance and toughness, however, it also has a defect that is inferior in corrosion-resistance. Further, the alloy cast iron disclosed in the Japanese patent application No. 9-307951 is outstanding in abrasion-resistance and impact-resistance; however, it also has a defect that it is a little inferior in corrosion-resistance and heat-resistance. The cast iron with all of abrasion-resistance, toughness, corrosion resistance, heat-resistance and processing ability has not been obtained yet. Therefore, an invention of cast iron which has outstanding corrosion-resistance and heat-resistance in addition to abrasion-resistance and toughness of the spheroidal graphite cast iron and the alloy cast iron disclosed in the Japanese patent application No. 9-307951 is desired.
Incidentally, stainless steel is known as a steel material with outstanding corrosion-resistance. Concretely, there is stainless steel prescribed with JJSG 5122 as follows; SCS12, SCS13, SCS19, and SCS21 of representative 18Cr-8Ni system, SCS14 of 18Cr-11Ni-Mo system, SCS11 of high Cr-Ni system, SCS1 and SCS2 of 13Cr, and high Cr system. These kinds of stainless steel comprise more than 12% of Cr and has the structure which protects from rust with a surface of steel wherein precise oxide such as FeO, Cr2O3 and NiO is crystallized after passivation caused by oxygenation of Cr.
Also, said stainless steel such as 18Cr-8Ni system has outstanding heat-resistance in addition to outstanding corrosion-resistance, thus it is used as heat-resisting steel widely in the field of boilers, turbines and jet engines. These kinds of stainless steel composed with Cr which rises recrystallization temperature and makes creep strength larger by depositing carbide and nitride. The necessary proportion of proposed Cr is 8% when working temperature is below 700xc2x0 C. and is more than 20% when working temperature is at 1000xc2x0 C.
Then, after continuing a devoted study of the alloy cast iron further, the present inventors have come to invent that not only abrasion-resistance and toughness but also outstanding corrosion-resistance and heat-resistance which are equal to what the stainless steel has and outstanding processing ability, can be given by crystallizing only spheroidal VC carbide, and that corrosion-resistance and heat-resistance can be improved more by mixing specific amount of special additives apart from necessary components.
The invention as set forth in claim 1 relates to stainless spheroidal carbide cast iron: comprising of Fe as its main component, C 0.6xcx9c4.0% and V 4xcx9c15% as its necessary components, P 0.01xcx9c0.15%, S 0.01xcx9c0.05%, and Al 0.05xcx9c1.0% as bubble assistants and Ni 4xcx9c15%, Si 0.2xcx9c4.5%, Cr 13xcx9c30%, and Mn 0.2xcx9c1.5% as anticorrosion matrix formers in weight %; produced by the process that minute spheroidal space of gas (hydrogen) bubble is dispersed substantially equally into molten metal positively by high temperature melting at 1950xcx9c2073 K which is the bubbling reaction temperature, and spheroidal vanadium carbide of a covalent bond is crystallized inside of the spheroidal space.
The invention as set forth in claim 2 relates to the stainless spheroidal carbide cast iron: comprising of Fe as its main component, C 0.6xcx9c4.0% and V 4xcx9c15% as its necessary components, P 0.01xcx9c0.15%, S 0.01xcx9c0.05%, and Al 0.05xcx9c1.0% as bubble assistants, and Si 0.2xcx9c4.5%, Cr 13xcx9c30%, Mn 0.2xcx9c1.5%, and Ni and/or Co 4xcx9c15% as anticorrosion matrix formers in weight %; produced by the process that minute spheroidal space of gas (hydrogen) bubble is dispersed substantially equally into molten metal positively by high temperature melting at 1950xcx9c2073 K which is the bubbling reaction temperature, and spheroidal vanadium carbide of a covalent bond is crystallized inside of the spheroidal space.
The invention as set forth in claim 3 relates to the stainless spheroidal carbide cast iron as set forth in claim 1 comprising a mixture of said alloy elements and at least more than one kind selected from additives (a)xcx9c(d) as follows: (a) Mo 0.05xcx9c15%; (b) Ti 0.01xcx9c5%; (c) B 0.01xcx9c2%; and (d) at least more than two kinds of alloy elements selected from Cu, W, Zr, Co, Nb, Ta and Y 0.2xcx9c5%.
The invention as set forth in claim 4 relates to the stainless spheroidal carbide cast iron as set forth in claim 2 comprising a mixture of said alloy elements and at least more than one kind selected from additives (a)xcx9c(d) as follows: (a) Mo 0.05xcx9c15%; (b) Ti 0.01xcx9c5%; (c) B 0.01xcx9c2%; and (d) at least more than two kinds of alloy elements selected from Cu, W, Zr, Co, Nb, Ta and Y 0.2xcx9c5%.
The invention as set forth in claim 5 relates to the stainless spheroidal carbide cast iron as set forth in claim 1 comprising a mixture of said alloy elements and at least more than one kind selected from additives (a)xcx9c(d) as follows: (a) Mo 0.05xcx9c5%; (b) Ti 0.01xcx9c1.0%; (c) B 0.01xcx9c0.5%; (d) at least more than two kinds of alloy elements selected from Cu, W, Zr, Co, Nb, Ta and Y 0.2xcx9c10%.
The invention as set forth in claim 6 relates to the stainless spheroidal carbide cast iron as set forth in claim 2 comprising a mixture of said alloy elements and at least more than one kind selected from additives (a)xcx9c(d) as follows: (a) Mo 0.05xcx9c5%; (b) Ti 0.01xcx9c1.0%; (c) B 0.01xcx9c0.5%; (d) at least more than two kinds of alloy elements selected from Cu, W, Zr, Co, Nb, Ta and Y 0.2xcx9c10%.
Providing this invention can solve said all problems.